JP2006099947A - Optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device in which two or more diffraction gratings capable of relaxing the influence of variation of environmental temperature can be realized with a single optical element. <P>SOLUTION: The optical head device comprises a light source 1, a variable diffraction element 2 which diffracts a part of luminous flux emitted by the light source to form a main beam and two sub-beams, an optical device 3 which transmits each beam emitted from the variable diffraction element 2 and also reflects each return light beam reflected by the information recording surface 7a of an optical disk and returned, and guides it to a photodetector 8, a collimator lens 4, an aperture 5, an objective lens 6, and the photo detector 8 for detecting the above each return light beam. The optical head device has a configuration which can simultaneously apply two or more spatial period pattern voltages to the variable diffraction element 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical head device in which a diffraction grating needs to be switched when recording or reproduction is performed on an optical recording medium (hereinafter referred to as an optical disk) such as a CD or a DVD.

Conventionally, an electrode having two different electrode patterns in order to avoid providing a plurality of diffraction gratings in an optical head device when information is recorded on or reproduced from an optical disc having a different track pitch standard on the information recording surface. A technique is disclosed in which different diffraction patterns are formed by applying different spatial pattern voltages to a liquid crystal using, for example (see Patent Document 1 and Patent Document 2).
FIG. 6 is an explanatory diagram conceptually showing the configuration of the liquid crystal diffraction element disclosed in Patent Document 1. In FIG.

  In FIG. 6, the liquid crystal 65 sandwiched between the transparent substrates 61 and 62 has different spatial patterns depending on the voltage applied between the transparent electrodes 63 a and 63 b having two different electrode patterns and the solid transparent electrode 64. It is designed to be applied. Here, the transparent electrode 63a and the transparent electrode 63b are insulated, and the applied voltage switching means 66 switches the object to which the voltage is applied between the transparent electrode 63a and the transparent electrode 63b and applies the voltage.

  A voltage having a spatial pattern corresponding to the electrode pattern of the transparent electrode 63a or the transparent electrode 63b to which the voltage is applied by the applied voltage switching unit 66 is applied to the liquid crystal 65. As a result, the liquid crystal diffraction element functions as a diffraction grating corresponding to this spatial pattern, and the liquid crystal diffraction element has a diffraction grating corresponding to the electrode pattern of the transparent electrode 63a to which the voltage is applied by the applied voltage switching means 66. Is realized.

On the other hand, the diffraction grating disclosed in Patent Document 2 has two liquid crystal display parts, and each liquid crystal display part is formed with a sprite-like transparent electrode. The liquid crystal display unit to which a voltage is applied functions as a diffraction grating, and the liquid crystal display unit to which no voltage is applied functions as a transparent flat plate. Switching of the diffraction grating is performed by switching a liquid crystal display unit to which a voltage is applied.
JP-A-4-283430 JP-A-9-282684

  However, in such an optical head device having a conventional liquid crystal diffraction grating, the liquid crystal diffraction grating is formed only by the liquid crystal portion to which voltage is applied and the liquid crystal portion to which voltage is not applied, so that the diffraction efficiency varies with the environmental temperature. There was a problem that it fluctuated greatly.

  The present invention has been made to solve such a problem, and provides an optical head device capable of realizing a plurality of diffraction gratings that can alleviate the influence of fluctuations in environmental temperature with a single optical element. is there.

In view of the above points, the invention according to claim 1 is directed to a light source, a variable diffraction element capable of switching a diffraction pattern for diffracting a passing light beam, and light emitted from the variable diffraction element on an optical recording medium. An optical recording medium, and an optical detector that detects light collected by the objective lens and reflected by the optical recording medium, and records or reproduces information on the optical recording medium. In the optical head device, the variable diffractive element has a plurality of transparent electrodes for applying an electric signal, and switches the transparent electrode to switch the diffraction pattern by applying the electric signal. A plurality of stripe-shaped electrodes are alternately combined on the same surface, and each set of stripe-shaped electrodes has a potential different from that of other sets of stripe-shaped electrodes. Door can be.
With this configuration, each transparent electrode is composed of a plurality of sets of striped electrodes, and each set of striped electrodes can have a different potential from other sets of striped electrodes. Since the degree of freedom to apply a voltage to an unapplied portion has increased, it is possible to realize an optical head device capable of realizing a plurality of diffraction gratings that can alleviate the influence of fluctuations in environmental temperature with a single optical element.

  According to a second aspect of the present invention, there is provided a light source, an objective lens for condensing the light beam emitted from the light source on the optical recording medium, and light detection for detecting the light beam collected by the objective lens and reflected by the optical recording medium. A beam splitter that multiplexes the light beam propagating from the light source to the objective lens and demultiplexes the light beam propagated from the objective lens to the photodetector, and a variable diffraction element that can switch a diffraction pattern that diffracts the passing light beam In the optical head device that records or reproduces information with respect to the optical recording medium, the variable diffraction element includes an optical path between the light source and the optical recording medium, and the optical recording medium and the photodetector. A plurality of transparent electrodes that are arranged in at least one of the optical paths between the two and apply an electric signal, and switch the transparent electrode to apply the electric signal. Can switch at least one of the diffraction pattern and diffraction efficiency, and each of the transparent electrodes is formed by alternately combining a plurality of striped electrodes on the same plane, The electrodes can be at a different potential than the other sets of striped electrodes.

  According to a fifth aspect of the present invention, in the first aspect, the variable diffractive element includes at least two opposing transparent substrates, a liquid crystal sandwiched between the transparent substrates, and the liquid crystal side of the transparent substrates. A transparent electrode having a striped electrode pattern in which ribbon-shaped electrodes are periodically arranged, and each of the transparent electrodes constitutes each of the transparent electrodes. Every other ribbon electrode is electrically connected and divided into two sets of stripe electrodes that can be set to different potentials, and at least one of the pitch and direction of the stripe electrodes on one transparent substrate Has a different configuration from at least one of the pitch and direction of the striped electrodes of the other transparent substrate.

  With this configuration, in addition to the effect of claim 1, the variable diffractive element has a liquid crystal and a plurality of sets of striped transparent electrodes provided at both ends of the liquid crystal, and can be set to different potentials for each set. It is possible to realize an optical head device whose characteristics can be easily adjusted by an electric signal.

  In addition, an invention according to claim 6 is the structure according to claim 1, wherein the average thickness of each of the transparent substrates is 100 times or more the thickness of the liquid crystal sandwiched between the transparent substrates. .

  With this configuration, in addition to the effect of the fifth aspect, the average thickness of each transparent substrate is set to 100 times or more the thickness of the liquid crystal, so that the variable diffraction due to the volume change of the liquid crystal having a larger expansion coefficient than that of the solid. It is possible to realize an optical head device capable of suppressing the element from becoming a convex lens or a concave lens and within a practical range.

  According to a seventh aspect of the present invention, the variable diffraction according to any one of the first to sixth aspects, wherein the variable diffraction is performed when recording or reproduction is performed on an optical recording medium having a different track pitch standard on the information recording surface. It has a configuration provided with an electric signal switching means for switching the electric signal applied to the element to diffract the light beam emitted from the light source into a main beam and two sub beams suitable for the track pitch of the information recording surface. Yes.

  According to this configuration, in addition to the effect of any one of claims 1 to 6, the electric signal switching means can convert the light beam incident on the variable diffraction element into a main beam and two sub beams suitable for the track pitch of the information recording surface. Thus, since the electric signal applied to the variable diffraction element is switched, an optical head device capable of appropriately recording or generating information on a plurality of optical recording media having different standards can be realized.

  In the present invention, each transparent electrode is composed of a plurality of sets of stripe electrodes, and each set of stripe electrodes can be set to a different potential from other sets of stripe electrodes. Since the degree of freedom to apply a voltage to an unapplied portion has increased, it is possible to provide an optical head device capable of realizing a plurality of diffraction gratings that can alleviate the influence of fluctuations in environmental temperature with a single optical element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a diagram showing a conceptual configuration of an optical head device according to an embodiment of the present invention. In FIG. 1, an optical head device 100 includes a light source 1 that emits a light beam having a predetermined wavelength, and a variable diffraction that diffracts a part of the light beam emitted from the light source 1 into three beams including a main beam and two sub beams. The above three beams emitted from the element 2 and the variable diffraction element 2 are transmitted, and the return light of the three beams reflected and returned from the information recording surface 7a of the optical disc 7 is reflected to the photodetector 8. A beam splitter 3 for guiding, a collimator lens 4 for converting an incident light beam into substantially parallel light, an aperture 5, an objective lens 6, and a photodetector 8 for detecting return light of the three beams are provided.

  A part of the light beam emitted from the light source 1 is diffracted by the variable diffraction element 2 into three beams, which are a main beam and two sub beams. The beam splitter 3, the collimator lens 4, the diaphragm 5, and the objective lens 6 are transmitted in this order. Then, the light is condensed on the information recording surface 7 a of the optical disk 7. The above three beams condensed on the information recording surface 7a of the optical disc 7 are reflected by the information recording surface 7a, pass through the objective lens 6, the aperture 5 and the collimator lens 4, and are reflected by the beam splitter 3, and are reflected by the light. The detector 8 is entered.

  Here, the output signal of the photodetector 8 is used to generate a read signal, a focus error signal, and a tracking error signal of information recorded on the optical disk recording surface 7a of the optical disk 7. The optical head device 100 includes a mechanism (focus servo) that controls the lens in the optical axis direction based on the focus error signal, and a lens that is substantially perpendicular to the optical axis based on the tracking error signal. Although a control mechanism (tracking servo) is provided, it is omitted in the configuration shown in FIG.

  The light source 1 is composed of, for example, a semiconductor laser, and emits a divergent light beam having a wavelength in the vicinity of 650 nm and linearly polarized light. In the above description, the light source 1 is configured to emit a light beam having a wavelength near 650 nm. However, the present invention is not necessarily limited to a configuration in which the light source 1 emits a light beam having a wavelength near 650 nm. The configuration may be such that a light beam having a wavelength near 400 nm, a light beam having a wavelength near 780 nm, or a light beam having another wavelength is emitted. Here, the wavelength near 400 nm, the wavelength near 650 nm, and the wavelength near 780 nm mean wavelengths in the ranges of 385 nm to 430 nm, 630 nm to 670 nm, and 760 nm to 800 nm, respectively.

  The light source 1 is configured to emit light beams of two or three wavelengths, and two or three semiconductor laser chips are mounted on the same substrate in the same package, so-called hybrid type two-wavelength laser light source or The light source 1 may be configured to form a three-wavelength laser light source. The light source 1 is also a monolithic type two-wavelength laser light source having two light emitting points that emit different wavelengths (for example, see Japanese Patent Application Laid-Open No. 2004-39898) or a monolithic type having three light emitting points. The three-wavelength laser light source may be used.

  FIG. 2 is a cross-sectional view schematically showing an example of the structure of the variable diffraction element constituting the optical head device according to the embodiment of the present invention. The variable diffraction element 2 includes a pair of transparent substrates 21, 22, stripe-shaped transparent electrodes 23, 24 formed on the opposing surfaces of the transparent substrates 21, 22, and a liquid crystal sandwiched between the transparent substrates 21, 22. 25, a sealing material 26 for sealing the liquid crystal 25 between the transparent substrates 21 and 22, and forming a liquid crystal cell, and a flexible circuit board 27 for applying a voltage to the transparent electrodes 23 and 24.

  Here, the liquid crystal 25 is sandwiched between the surfaces on which the transparent electrodes 23 and 24 of the transparent substrates 21 and 22 are formed. FIG. 3 is an explanatory diagram for explaining electrode patterns of the transparent electrodes 23 and 24 formed on the transparent substrates 21 and 22. The transparent electrodes 23 and 24 have different electrode patterns. Hereinafter, it is assumed that the transparent electrode 23 has the electrode pattern shown in FIG. 3A and the transparent electrode 24 has the electrode pattern shown in FIG.

  As shown in FIG. 3, the transparent electrodes 23 and 24 have a striped electrode pattern in which ribbon-shaped electrodes (hereinafter referred to as ribbon-shaped electrodes) are periodically arranged. However, the arrangement pitch of the ribbon electrodes of the transparent electrodes 23 and 24 is different from each other. Further, the stripe electrode pattern of the transparent electrode 23 and the stripe electrode pattern of the transparent electrode 24 have a predetermined angle (hereinafter referred to as an opposing inclination angle) in a state where the transparent substrate 21 and the transparent substrate 22 face each other. It is formed on each of the transparent substrates 21 and 22 so as to make up.

  3, each transparent electrode 23 when viewed from the surface direction of the transparent substrate 22 facing the surface on which the transparent electrode 23 of the transparent substrate 21 is formed, with the transparent substrate 21 and the transparent substrate 22 facing each other. The state of 24 electrode patterns is conceptually represented. Here, the opposing inclination angle formed by the transparent electrode 23 and the transparent electrode 24 is set within a range of 0.2 degrees to 5 degrees. Preferably, the opposing inclination angle is set within a range from 0.5 degrees to 1.5 degrees.

  As shown in FIG. 3, the ribbon electrodes of the transparent electrodes 23 and 24 are connected to each other by wiring, and are divided into two sets of stripe electrodes. As a result, the pitch of the striped electrodes (the period of arrangement of the ribbon-shaped electrodes) is the distance obtained by combining the width of the ribbon-shaped electrodes and the gap between the ribbon-shaped electrodes in the configuration shown in FIG. Twice as much. However, the configuration of the striped electrode is not limited to the above example, and various configurations such as changing the width between adjacent ribbon electrodes constituting the striped electrode can be employed.

  In this case, the pitch of the striped electrodes is a cycle of a combination of a plurality of ribbon electrodes having different shapes and arrangements. Here, by changing the width of the ribbon electrode every other line, that is, by alternately arranging the thick ribbon electrode and the thin ribbon electrode, the electric field distribution in the liquid crystal can be adjusted by changing the electrode width, Generation of higher-order diffracted light such as ± second-order diffracted light when light is diffracted can be reduced. Normally used beams are only 0th order transmitted light (0th order diffracted light) and ± 1st order diffracted light, and it is preferable that the number of higher order diffracted light is small.

Each of the transparent electrodes 23 and 24 functions as a reference electrode with respect to the other transparent electrodes 23 and 24 when the same voltage is applied. That is, when the same voltage is applied to the transparent electrode 23, the transparent electrode 23 functions as a reference electrode for the other transparent electrode 24, and when the same voltage is applied to the transparent electrode 24, the transparent electrode 24 Functions as a reference electrode for the other transparent electrode 23.
Furthermore, the pitch of one of the transparent electrodes may be infinite so that substantially no diffraction pattern exists. In this case, the presence or absence of diffraction by the variable diffraction element is controlled depending on whether or not a voltage is applied.

  Here, although the pitch of each transparent electrode 23 and 24 may mutually differ, it shall be set in the range from 5 micrometers to 30 micrometers, respectively. Preferably, the pitch of the transparent electrodes 23 and 24 is set within a range of 10 μm to 20 μm. By setting the pitch of the transparent electrodes 23 and 24 as described above, the interval between the three spots formed by focusing the three beams on the optical disk 7 is within a range from 5 μm to 20 μm. And stable tracking characteristics can be realized.

  The transparent electrodes 23 and 24 are formed by depositing a thin film made of ITO or the like on the surfaces of the transparent substrates 21 and 22 and patterning it using a photolithography technique and an etching technique. Thin film deposition methods and electrode patterning methods are known and will not be described further. Although omitted in the configuration shown in FIG. 2, it is preferable to deposit an insulating film or an alignment film on the surfaces of the transparent electrodes 23 and 24.

  The liquid crystal 25 is aligned parallel to the transparent substrates 21 and 22 and is aligned in a direction determined by an alignment film or the like provided on the transparent substrates 21 and 22. The light source 1 and the variable diffraction element 2 are arranged so that the polarization direction of the emitted light beam coincides with the alignment direction on the incident surface of the liquid crystal 25. The alignment direction of the liquid crystal 25 can be set by adjusting the rubbing of the alignment film, and can also be set by obliquely depositing SiO or the like, or irradiating an ion beam. Hereinafter, it is assumed that at least an alignment film is formed on the transparent electrodes 23 and 24.

  The liquid crystal 25 may have a positive or negative dielectric anisotropy. Here, a liquid crystal having a positive dielectric anisotropy is one that moves so that liquid crystal molecules are parallel to the direction of the electric field when an electric field is applied. The liquid crystal molecules move so as to be perpendicular to the direction of the applied electric field. However, when a liquid crystal having a negative dielectric anisotropy is used, it is preferable to use an alignment film whose liquid crystal molecules are substantially perpendicular to the substrate when no voltage is applied.

  The use of a liquid crystal having a negative dielectric anisotropy is because liquid crystal molecules are aligned perpendicular to the transparent substrates 21 and 22 when no voltage is applied, so that transmitted light does not feel the birefringence of the liquid crystal. It is preferable because the polarization direction does not change depending on the polarization direction of incident light.

  The sealing material 26 keeps the distance between the transparent substrates 21 and 22 constant, and confines the liquid crystal 25 between the transparent substrates 21 and 22. Voltages V1a and V1b and V2a and V2b are applied to the transparent electrodes 23 and 24 of the variable diffraction element 2 through the flexible circuit board 27, respectively (see FIG. 3). Here, the voltage V1a is applied to one set of ribbon electrodes (hereinafter referred to as first stripe electrodes) of the transparent electrode 23, and the voltage V1b is applied to the other set of ribbon electrodes (hereinafter referred to as first stripe electrodes). Applied to a second stripe electrode).

  Similarly, the voltage V2a is applied to one set of ribbon-like electrodes (hereinafter referred to as a third stripe electrode) of the transparent electrode 24, and the voltage V2b is applied to the other set of ribbon-like electrodes (hereinafter referred to as the third stripe electrode). Applied to the fourth stripe electrode). If the set of ribbon electrodes is different, a voltage is generally applied so as to have a potential different from that of the other sets. However, in a predetermined case such as when the transparent electrodes 23 and 24 function as reference electrodes, the voltage differs. A voltage may be applied so as to be the same potential between a plurality of sets.

  The collimator lens 4 converts three beams, which are emitted from the variable diffraction element 2 and composed of a main beam and two sub beams, into substantially parallel light.

  The diaphragm 5 sets the numerical aperture NA by selectively restricting the aperture of the light beam from the light source 1. By providing the diaphragm 5, the numerical aperture can be adjusted when recording / reproducing is performed on two types of optical disks having different numerical apertures. Specifically, the numerical aperture NA is set to 0.65 for a light beam having a wavelength near 650 nm, and the numerical aperture NA is set to 0.50 for a light beam having a wavelength near 780 nm. To do. The diaphragm 5 includes a mechanical diaphragm and an optical diaphragm, and is not particularly limited.

  The objective lens 6 is a single lens whose aberration is corrected to such an extent that it can be used at the wavelength of the light beam emitted from the light source 1, so that the parallel light from the collimator lens 4 is condensed on the information recording surface 7 a of the optical disk 7. It has become. As the objective lens 6, for example, an objective lens disclosed in JP 2001-344798 A can be used.

  The optical disk 7 is a recording medium for recording and reproduction. For example, for a light beam having a wavelength near 650 nm, the optical disk 7 has a protective layer thickness of, for example, 0.6 mm and is converted into a light beam having a wavelength near 780 nm. For example, it has a protective layer thickness of 1.2 mm.

  The photodetector 8 receives the return light of the three beams from the information recording surface 7a of the optical disc 7, and reads a read signal, a focus error signal, and a tracking error signal according to the information recorded on the information recording surface 7a. Each signal is generated and output to the outside.

  Hereinafter, the optical characteristics of the variable diffraction element 2 will be described with reference to the drawings. FIG. 4 is a diagram illustrating an example of the relationship between the voltage applied to the transparent electrodes 23 and 24 constituting the variable diffraction element 2 and the change in the optical path length of the light transmitted through the liquid crystal 25. When a voltage is applied to the liquid crystal 25, the alignment direction changes in a direction in which the liquid crystal molecules are perpendicular to the transparent substrates 21 and 22, so that the refractive index with respect to light polarized in a direction substantially parallel to the alignment direction of the liquid crystal 25 is small. Thus, the optical path length is shortened.

  In FIG. 4, the solid line shows the relationship between the applied voltage obtained at room temperature and the change in optical path length, and the broken line shows the relationship between the applied voltage and the change in optical path length at 80 degrees. Here, when the diffraction grating is formed differently from the voltage V1a and the voltage V1b applied to the transparent electrode 23 on the transparent substrate 21, the voltage V2a and the voltage applied to the transparent electrode 24 on the transparent substrate 22 as described above. V2b is made equal. Hereinafter, when the voltage V2a is equal to the voltage V2b, this voltage is referred to as V2.

At this time, the voltage ΔV1a applied to the portion of the liquid crystal 25 sandwiched between the first stripe electrode and the transparent electrode 24 (hereinafter referred to as the first stripe region) is V1a−V2, and the liquid crystal 25 Among them, a voltage ΔV1b applied to a portion sandwiched between the second stripe electrode and the transparent electrode 24 (hereinafter referred to as a second stripe region) is V1b−V2.
As a result, the light flux incident on the first stripe region of the liquid crystal 25 and the light flux incident on the second stripe region of the liquid crystal 25 have different optical path length differences specified based on the relationship shown in FIG. It will be.

  Hereinafter, the optical path length difference with respect to the light beam incident on the first stripe region of the liquid crystal 25 is φ1a, and the optical path length difference with respect to the light beam incident on the second stripe region of the liquid crystal 25 is φ1b. In this way, by making the voltage V1a applied to the first stripe electrode different from the voltage V1b applied to the second stripe electrode, the optical path length with respect to the light beam incident on the variable diffraction element 2 becomes the pitch of the transparent electrode 23. The incident light flux that has been modulated with a period determined by ## EQU1 ## undergoes phase modulation with (φ1a−φ1b = Δφ1) as a phase modulation amplitude, and is diffracted according to the phase modulation amplitude (φ1a−φ1b).

  Here, even when any one of the voltage V1a applied to the first stripe electrode and the voltage V1b applied to the second stripe electrode is equal to the voltage V2 applied to the transparent electrode 24, The light beam incident on the variable diffraction element 2 can be phase-modulated and diffracted. Hereinafter, a case where the voltage V1b applied to the second stripe electrode is made equal to the voltage V2 applied to the transparent electrode 24 will be described as an example.

In this case, the voltage ΔV1a applied between the first stripe electrode and the transparent electrode 24 takes a predetermined value other than zero, and the voltage ΔV1b applied between the second stripe electrode and the transparent electrode 24 is It becomes zero. Here, the voltage ΔV1b applied between the second stripe electrode and the transparent electrode 24 becomes zero, and the optical path length difference is smaller than the threshold voltage _Vth that starts changing with respect to the voltage. The threshold voltage _Vth is about 1.3 Vrms in the example shown in FIG. As shown in FIG. 4, the change in the optical path length due to the change in the environmental temperature is larger as the voltage is lower, and is particularly great at a voltage equal to or lower than the threshold voltage _Vth . Therefore, the phase modulation received by the light beam incident on the liquid crystal 25 is also greatly affected by the fluctuation of the environmental temperature. Therefore, the influence of environmental temperature fluctuations also increases on the phase modulation received by the light beam incident on the liquid crystal 25, and the temperature fluctuations of diffraction efficiency also increase.

On the other hand, the voltage ΔV1a applied between the first stripe electrode and the transparent electrode 24 and the voltage ΔV1b applied between the second stripe electrode and the transparent electrode 24 are each other than zero. When the values are different, the influence of the fluctuation of the environmental temperature on the optical path length difference φ1b can be reduced, and the influence of the fluctuation of the environmental temperature on the phase modulation received by the light beam incident on the liquid crystal 25 can be reduced.
In particular, as shown in FIG. 4, the voltage ΔV1a and the voltage ΔV1b are set to a threshold voltage _Vth or more at which an optical path length difference of about 1.3 Vrms or more starts to change with respect to the voltage. Is preferable because it can be effectively reduced.
Furthermore, as shown in FIG. 4, by setting the region where the optical path length difference is about 1.6 Vrms or more and about 3 Vrms or less to change substantially linearly with respect to the voltage, the influence of the fluctuation of the environmental temperature is more effectively prevented. It is preferable because it can be reduced.
This is due to the fact that, in the above region, the slope of the change in the optical path length difference with respect to the voltage becomes smaller due to fluctuations in the environmental temperature.

  Similarly, when the diffraction grating is formed differently from the voltage V2a and the voltage V2b applied to the transparent electrode 24 on the transparent substrate 22, the voltage V1a and the voltage applied to the transparent electrode 23 on the transparent substrate 21 as described above. V1b is made equal. Hereinafter, when the voltage V1a is equal to the voltage V1b, this voltage is referred to as V1.

At this time, the voltage ΔV2a applied to the portion of the liquid crystal 25 sandwiched between the third stripe electrode and the transparent electrode 23 (hereinafter referred to as the third stripe region) is V2a−V1, and the liquid crystal 25 Among them, the voltage ΔV2b applied to the portion sandwiched between the fourth stripe electrode and the transparent electrode 23 (hereinafter referred to as the fourth stripe region) is V2b−V1.
As a result, the light flux incident on the third stripe region of the liquid crystal 25 and the light flux incident on the fourth stripe region of the liquid crystal 25 have different optical path length differences specified based on the relationship shown in FIG. It will be.

  Hereinafter, the optical path length difference with respect to the light beam incident on the third stripe region of the liquid crystal 25 is φ2a, and the optical path length difference with respect to the light beam incident on the fourth stripe region of the liquid crystal 25 is φ2b. In this way, by making the voltage V2a applied to the third stripe electrode different from the voltage V2b applied to the fourth stripe electrode, the optical path length with respect to the light beam incident on the variable diffraction element 2 becomes the pitch of the transparent electrode 24. The incident light beam that is modulated with a period determined by the above is subjected to phase modulation with a phase modulation amplitude of (φ2a−φ2b = Δφ2), and is diffracted according to the phase modulation amplitude (φ2a−φ2b).

Here, the voltage applied to the transparent electrodes 23 and 24 is preferably not a direct current but a rectangular alternating current.
As described above, by changing the voltage application method applied to the transparent electrodes 23 and 24, the variable diffraction element 2 can be made into a diffraction grating having a different grating pitch and stripe direction. In addition, by adjusting the method of applying the voltage applied to the transparent electrodes 23 and 24, it is possible to realize the variable diffraction element 2 that can reduce the influence of environmental temperature fluctuations.

FIG. 5 is a diagram illustrating an example of phase modulation amplitude characteristics of transmittance and diffraction efficiency obtained in the variable diffraction element 2 configured as described above. In this example, the wavelength is 660 nm.
In FIG. 5, the solid line represents the phase modulation amplitude characteristic of the transmittance (0th order diffraction), and the broken line represents the phase modulation amplitude characteristic of the first order diffraction efficiency. When the intensity of the main beam and the intensity of the two sub beams are specified, the required phase modulation amplitude can be determined based on the curve shown in FIG. This is effective when the intensity of the main beam and the intensity of the two sub beams are changed to desired values.

  Specifically, the optimum value differs between the intensity of the main beam and the intensity of the two sub beams when writing to the optical disk 7 and when reading from the optical disk 7. When the intensity of each beam is to be changed, the intensity of each beam can be changed by changing the diffraction efficiency by changing the voltage applied to each transparent electrode 23, 24.

  For example, when writing to the optical disc 7, that is, when a large power is required for the main beam, the transmitted light amount (0th order diffracted light amount) is increased to increase the writing power by reducing the diffraction efficiency, When reading from the optical disc 7, that is, when a large power is not required for the main beam, by increasing the diffraction efficiency, the first-order diffracted light amount is increased and the light amount of the tracking sub-beam is increased, which is resistant to noise. Reproduction characteristics can be realized.

(Second Embodiment)
Next, the conceptual configuration of the optical head device according to the second embodiment of the present invention is different from the configuration of the optical head device 100 according to the first embodiment of the present invention shown in FIG. The point is different.
In the optical head device 100 according to the first embodiment, the variable diffractive element 2 is disposed in the optical path between the light source 1 and the beam splitter 3, and a part of the light beam emitted from the light source 1 is diffracted by the variable diffractive element 2. Thus, three beams composed of a main beam and two sub beams are generated.
In the optical head device 100 according to the second embodiment, the variable diffractive element 2 is disposed in the optical path between the beam splitter 3 and the photodetector 8, and is reflected back from the information recording surface 7a of the optical disc 7. A part of the light beam is diffracted by the variable diffraction element 2 and condensed onto a plurality of light receiving surfaces of the photodetector 8.

Since the other arrangement and configuration of the optical head device are the same as those of the optical head device 100 according to the first embodiment, the same components are denoted by the same reference numerals, and the description thereof is omitted.
When a focus servo or tracking servo using the astigmatism method is employed, an optical element that generates astigmatism such as a cylindrical lens is disposed in the optical path between the beam splitter 3 and the photodetector 8. Is common.

  The variable diffraction element used in the optical head device according to the second embodiment of the present invention has the same configuration as that of the first embodiment. When recording or playing back optical recording media with different track pitch standards on the information recording surface, the electrical signal applied to the variable diffractive element is switched to detect the focus servo and tracking servo optimal for the optical recording medium. The stripe-like electrode pattern of the variable diffraction element is designed so as to generate the diffraction pattern.

  A diffractive element is disposed in the optical path between the beam splitter 3 and the light detector 8, and 0th-order diffracted light (transmitted light) and ± 1st-order diffracted light are used as optical signals for optical disc recording / reproduction, focus servo and tracking servo detection. What is used is known as a hologram beam splitter system. In a diffraction element used in the hologram beam splitter method, a diffraction grating region is generally divided into a plurality of spaces within an incident light beam plane, and the pitch and stripe direction of the diffraction grating are different in each region. In addition, a hologram pattern that imparts a lens function and a wavefront aberration generation function to the diffracted light may be obtained by providing a distribution in the pitch and stripe direction of the diffraction grating in each region. The stripe-shaped electrode pattern that generates the diffracted light of the variable diffraction element 2 used in the present embodiment can also use such a hologram beam splitter type design configuration and hologram pattern.

  When the variable diffractive element 2 is arranged in the optical path between the light source 1 and the beam splitter 3, three beams composed of 0th order diffracted light (transmitted light: main beam) and ± 1st order diffracted light (two sub beams) are generated. However, in the case of this embodiment in which the variable diffractive element 2 is disposed in the optical path between the beam splitter 3 and the photodetector 8, both ± first-order diffracted light or Only one of them may be used as an optical signal.

  In the present embodiment, the variable diffraction element 2 is disposed in the optical path between the beam splitter 3 and the photodetector 8 so that the diffracted light in the middle of the forward light from the light source 1 to the optical disk 7 in the first embodiment. Since there is no decrease in the 0th-order transmitted light rate due to the generation, it is effective for an optical head device for recording that requires high efficiency of 0th-order diffracted light (transmitted light).

  In FIG. 2 and FIG. 3, two kinds of striped transparent electrodes 23 and 24 are used as variable diffraction elements used in the optical head device of the present invention, and applied electric signals (V1a, V1b, V2a, V2b) are switched. The state where the function of the diffraction grating is not expressed (when V1a = V1b and V2a = V2b) and the state where the function of one of the two types of diffraction gratings is expressed (V1a = V1b and V2a ≠ V2b, or , V1a ≠ V1b and V2a = V2b).

Thus, when a variable diffractive element that switches between a state in which diffracted light is generated and a state in which no diffracted light is generated in accordance with the applied voltage is obtained, a plurality of variable diffractive elements with different generated diffracted light are arranged in series. Without being limited to the type, it can be generated by switching the diffracted light of a plurality of diffraction gratings.
As a result, when recording or reproduction is performed on a plurality of optical recording media having different track pitch standards on the information recording surface, an electric signal applied to the variable diffraction element composed of the plurality of diffraction gratings is switched to Signal detection optimal for the recording medium is possible.

(Third embodiment)
Next, examples of the optical head device 100 according to the third embodiment of the present invention will be described. The configuration of the optical head device 100 according to the first embodiment of the present invention shown in FIG.
In the optical head device 100 according to the first embodiment, the variable diffractive element 2 is disposed in the optical path between the light source 1 and the beam splitter 3, and a part of the light beam emitted from the light source 1 is diffracted by the variable diffractive element 2. Thus, three beams composed of a main beam and two sub beams are generated.
In the optical head device 100 according to the third embodiment, the variable diffractive element 2 is arranged in the optical path between the beam splitter 3 and the objective lens 6, and the forward light emitted from the light source 1 passes through the variable diffractive element 2. Then, the return light that is focused on the optical disk 7 by the objective lens 6 and reflected back from the information recording surface 7 a of the optical disk is transmitted through the variable diffraction element 2 again and guided to the photodetector 8.

  At this time, it is assumed that the light transmitted through the variable diffractive element 2 can change the light efficiency of the 0th order transmitted light by changing the diffraction efficiency by the voltage applied to the variable diffractive element 2. For example, in a state where the diffraction efficiency is low or not diffracted, the 0th-order diffracted light amount that passes through the variable diffraction element 2 increases, and the light amount that reaches the optical disc 7 increases. On the other hand, the diffraction efficiency is increased, the 0th-order diffracted light quantity transmitted through the variable diffraction element 2 is reduced, and the light quantity reaching the optical disk 7 can be reduced while the emitted light quantity from the semiconductor laser as the light source is increased. .

  When writing to the optical disk 7, it is necessary to increase the amount of light reaching the optical disk, and it is preferable to reduce the diffraction efficiency of the variable diffraction element or to prevent diffraction. Further, when reading the information recorded on the information recording surface 7a of the optical disc, it is necessary to reduce the amount of light reaching the optical disc. At this time, if the amount of light emitted from the semiconductor laser as the light source 1 is reduced, the oscillation of the semiconductor laser becomes unstable and noise increases, which adversely affects the reading performance. Therefore, by increasing the diffraction efficiency of the variable diffractive element 2 and reducing the 0th-order transmitted light amount reaching the optical disk, the optical disk can be read with low noise while increasing the emitted light amount of the semiconductor laser as the light source. In addition, the amount of light that should reach the optical disc differs greatly between an optical disc having two information recording surfaces and an optical disc having a single layer. In such a case, the change in the amount of light by the variable diffraction element is effective.

  In the present embodiment, the function of changing the diffraction efficiency of the variable diffraction element or switching between a diffracting state and a non-diffracting state is important. As shown in FIGS. 4 and 5, by adjusting the potential difference between the stripe electrodes, the optical path length between the stripe electrodes of the liquid crystal changes, and the diffraction efficiency can be changed. In FIGS. 2 and 3, two types of transparent electrodes 23 and 24 in a stripe shape are used, and the electric signal (V1a, V1b, V2a, V2b) to be applied is switched so that the function of the diffraction grating does not appear (V1a = V1b). And a state in which the function of one of the two types of diffraction gratings is manifested (when V1a = V1b and V2a ≠ V2b, or when V1a ≠ V1b and V2a = V2b). .

  Thus, when a variable diffractive element that switches between a state in which diffracted light is generated and a state in which no diffracted light is generated in accordance with the applied voltage is obtained, a plurality of variable diffractive elements with different generated diffracted light are arranged in series. Without being limited to the type, it can be generated by switching the diffracted light of a plurality of diffraction gratings. Further, any one of the striped transparent electrodes 23 and 24 may be a flat reference electrode instead of the striped divided electrode so that the pitch of the striped electrode becomes infinite.

Further, by arranging a quarter wavelength plate between the variable diffraction element and the objective lens, the forward linearly polarized light emitted from the light source 1 is transmitted through the quarter wavelength plate and reflected again by the optical disk. By transmitting through the quarter-wave plate, the polarization direction of the return path can be orthogonal to the linear polarization direction of the forward path.
This makes it possible to make the polarization directions orthogonal in the forward path and the return path that pass through the variable diffraction element. The variable diffraction element using the liquid crystal of the present invention has a polarization direction of light that can change diffraction efficiency and a polarization direction that does not change. The polarization direction capable of changing the diffraction efficiency is matched with the forward polarization direction, and the light in the backward polarization direction is set to have a low diffraction efficiency and a high transmittance. That is, only the 0th-order diffracted light in the forward path can be made variable by changing the voltage application state to the variable diffractive element, and the light in the return path can be guided to the photodetector with high 0th-order diffracted light. This makes it possible to vary the forward transmittance according to the type of optical disk and the state of writing and reading, and to guide the light to the optical disk with the optimum light intensity. The light reflected from the optical disk is independent of the type of optical disk. Since the light can be transmitted through the variable diffraction element with high transmittance and guided to the photodetector with high utilization efficiency, it is preferable that an optical signal including information on the optical disk can be detected with a good SN ratio.

  Specific examples based on the above-described embodiments of the present invention will be described below.

[Example 1]
As shown in FIG. 1, an optical head device 100 according to Example 1 includes a light source 1 that emits a light beam having a predetermined wavelength, and a main beam and two sub beams that diffract part of the light beam emitted from the light source 1. The variable diffractive element 2 having three beams and the three beams emitted from the variable diffractive element 2 are transmitted and the return light of the three beams reflected and returned from the information recording surface 7a of the optical disc 7 is reflected. A beam splitter 3 that leads to a photodetector 8, a collimator lens 4 that converts an incident light beam into substantially parallel light, an aperture 5, an objective lens 6, and a photodetector 8 that detects return light of the three beams. With.

  In Example 1, the wavelength of the light beam emitted from the light source 1 is 660 nm, the thickness of the liquid crystal 25 is 4 μm, and the refractive index difference Δn depending on the polarization direction of the liquid crystal 25 is 0.15. Further, it is assumed that the average thickness of each of the transparent substrates 21 and 22 is 100 times or more the thickness of the liquid crystal 25 sandwiched between the transparent substrates 21 and 22. This is because the deformation of the element increases as the volume change due to thermal expansion increases in proportion to the thickness of the liquid crystal 25, and the thicker the liquid crystal 25, the higher the rigidity of the substrate needs to be. And the influence by the difference in the expansion coefficient of the liquid crystal 25 and the sealing material 26 can be eliminated by making the average thickness of each transparent substrate 21 and 22 100 times or more of the thickness of the liquid crystal 25. Furthermore, it is preferable that the thickness of the liquid crystal 25 is set to 1/150 or less of the average thickness of the transparent substrates 21 and 22 from the viewpoint of increasing the rigidity of the substrate.

  This will be described in detail below. Since the liquid crystal 25 is a liquid and the sealing material 26 is a solid, the expansion coefficients are significantly different. Therefore, in a configuration in which the liquid crystal substrates 21 and 22 are easily deformed due to the temperature change of the liquid crystal 25, the variable diffractive element 2 becomes a convex lens as the temperature rises. Conversely, the variable diffractive element 2 becomes a concave lens as the temperature decreases. To go. As a result, the focal point of the beam to be condensed on the optical disc 7 is displaced due to the influence of the temperature change.

  Here, by setting the average thickness of the transparent substrates 21 and 22 to 100 times or more the thickness of the liquid crystal 25, the rigidity of the transparent substrates 21 and 22 is increased, and it is possible to suppress the shape change to withstand practical use. did it. Further, it is preferable that the average thickness of each of the transparent substrates 21 and 22 is 150 times or more the thickness of the liquid crystal 25, whereby a higher effect can be obtained.

  As shown in FIG. 2, the variable diffraction element 2 constituting the optical head device 100 according to Example 1 is formed on each of the opposing surfaces of the pair of transparent substrates 21 and 22 and the two transparent substrates 21 and 22. Striped transparent electrodes 23, 24, liquid crystal 25 sandwiched between two transparent substrates 21, 22, sealing material 26 for sealing liquid crystal 25 between transparent substrates 21, 22 to form a liquid crystal cell, transparent And a flexible circuit board 27 for applying a voltage to the electrodes 23 and 24.

  The transparent substrates 21 and 22 are preferably transparent glass, but may be other inorganic substances and organic substances such as plastics. As shown in FIG. 3, the transparent electrodes 23 and 24 have a striped electrode pattern in which ribbon-like electrodes are periodically arranged. However, the period of arrangement of the ribbon electrodes of the transparent electrodes 23 and 24 is different from each other. In addition, the striped electrode pattern of the transparent electrode 23 and the striped electrode pattern of the transparent electrode 24 are formed on the transparent substrates 21 and 22 so that the opposing inclination angle is 1 degree.

  As shown in FIG. 3, the ribbon-like electrodes of the transparent electrodes 23 and 24 are connected by wiring at intervals of one each, and are divided into two groups. As a result, as shown in FIG. 3A, the pitch, which is the period of the arrangement of the ribbon electrodes in each group, is twice the distance of the combined width of the ribbon electrodes and the gap between the ribbon electrodes. . This pitch is twice the period of the arrangement of the ribbon-like electrodes before dividing into two groups. Here, the pitches of the transparent electrodes 23 and 24 are different from each other, and are 12 μm and 13 μm, respectively.

  The transparent electrodes 23 and 24 function as reference electrodes for the remaining transparent electrodes 23 and 24 when the same voltage is applied. In this embodiment, a first voltage application example and a second voltage application example are shown. In the first voltage application example, the third stripe electrode and the fourth stripe electrode are set to the same potential (hereinafter referred to as V2a = V2b = 0 Vrms), the transparent electrode 24 is used as a reference electrode, and the first stripe electrode is used. The potentials of the second stripe electrode and V2a were set to V1a = 1.7 Vrms and V1b = 2.25 Vrms with respect to the transparent electrode 24, respectively.

  In the second voltage application example, the first stripe electrode and the second stripe electrode are set to the same potential (hereinafter referred to as V1a = V1b = 0 Vrms), the transparent electrode 23 is used as a reference electrode, and the third stripe electrode is used. The potentials of the fourth stripe electrode and the transparent electrode 24 were set to V2a = 1.7 Vrms and V2b = 2.4 Vrms, respectively. By setting the potential to be applied to each stripe electrode in this way, as shown in FIG. 4, it is within a region where the influence of the fluctuation of the environmental temperature on the transmittance or diffraction efficiency can be effectively suppressed.

  The transparent electrodes 23 and 24 are formed by depositing a thin film made of ITO on the surfaces of the transparent substrates 21 and 22 and patterning the film using a photolithography technique and an etching technique. Thin film deposition methods and electrode patterning methods are known and will not be described further. Although omitted in the configuration shown in FIG. 2, an insulating film and an alignment film are deposited on the surfaces of the transparent electrodes 23 and 24.

  The liquid crystal 25 is aligned parallel to the transparent substrates 21 and 22 by an alignment film provided on the transparent substrates 21 and 22. The light source 1 and the variable diffraction element 2 are arranged so that the polarization direction of the emitted light beam coincides with the alignment direction on the incident surface of the liquid crystal 25. The alignment direction of the liquid crystal 25 is set by adjusting the rubbing of the alignment film. As the liquid crystal 25, a liquid crystal having positive dielectric anisotropy, that is, a liquid crystal molecule parallel to the direction of the electric field when an electric field is applied is used.

  The sealing material 26 keeps the distance between the transparent substrates 21 and 22 constant and confines the liquid crystal 25 between the transparent substrates 21 and 22. By applying a voltage to the transparent electrodes 23 and 24 provided in the variable diffraction element 2 via the flexible circuit board 27, the refractive index of the liquid crystal 25 sandwiched between the transparent substrates 21 and 22 is changed to the applied voltage distribution. Will change accordingly. When the incident light to the variable diffraction element 2 passes through the liquid crystal 25, the phase changes depending on the refractive index distribution in the liquid crystal 25, and therefore changes according to the voltage applied to the wavefront.

  In the first voltage application example (V1a = 1.7 Vrms, V1b = 2.25 Vrms, V2a = V2b = 0 Vrms), the optical path length change Δφ1 is 0.08 μm and is applied to the transparent electrode 23 on the transparent substrate 21. The diffraction efficiency obtained by the diffraction grating formed differently from the voltage V1a and the voltage V1b has a transmittance (0th-order diffraction efficiency) of 86% and a first-order diffraction efficiency of 5.7%.

  Similarly, in the second voltage application example (V1a = V1b = 0 Vrms, V2a = 1.7 Vrms, V2b = 2.4 Vrms), the optical path length change Δφ2 is 0.10 μm and is applied to the transparent electrode 24 on the transparent substrate 22. The diffraction efficiency obtained by using the diffraction grating formed differently from the voltage V2a and the voltage V2b to be transmitted has a transmittance (0th-order diffraction efficiency) of 78.5% and a first-order diffraction efficiency of 8.7%.

  As described above, since the transmittance (0th-order diffraction efficiency) in the first voltage application example is higher than the transmittance (0th-order diffraction efficiency) in the second voltage application example, the first voltage application By applying the voltage of the example, the power of the main beam can be increased, and a main beam suitable for recording information on the optical disk can be obtained. Similarly, since the first-order diffraction efficiency in the second voltage application example is higher than the first-order diffraction efficiency in the first voltage application example, by applying the voltage of the second voltage application example, The power can be increased, and a sub beam suitable for reproducing information from the optical disk can be obtained.

  Here, based on the difference in track pitch, the types of optical disks are classified into, for example, the following five groups. That is, the first group is CD, CD-ROM, CD-R, etc., the second group is DVD, DVD-R, DVD + R, etc., the third group is DVD-RAM, etc., and the fourth group is BLURAY (registered trademark). ) The disc is the HD-DVD (High Definition DVD) as the fifth group.

  Here, within each group, the track pitch is substantially the same. The single optical head device according to the embodiment of the present invention is effective when recording / reproducing is performed on an optical disk extending over these groups having different track pitches. In order to ensure such a function, when the optical head device of the present invention performs recording or reproduction on an optical recording medium having a different track pitch standard on the information recording surface, an electric signal applied to the variable diffraction element is applied. An electric signal switching means for diffracting the light beam emitted from the light source and switching it into a main beam and two sub beams suitable for the track pitch of the information recording surface may be used.

  In the above description, the variable diffractive element uses the main beam and the two side beams for the light beam emitted from the light source. However, the present invention is not limited to such a configuration, and diffraction is not possible. The present invention can be applied to all apparatuses configured to switch the lattice.

  As described above, in the optical head device according to the embodiment of the present invention, each transparent electrode is constituted by a plurality of sets of striped electrodes, and each set of striped electrodes is replaced with another set of striped electrodes. Therefore, a plurality of diffraction gratings that can alleviate the influence of fluctuations in environmental temperature can be realized with a single optical element. .

  In addition, since the variable diffractive element has a liquid crystal and a plurality of sets of striped transparent electrodes provided at both ends of the liquid crystal and can be set to different potentials for each set, the optical characteristics can be easily adjusted by an electric signal.

  In addition, since the average thickness of each transparent substrate is set to 100 times or more the thickness of the liquid crystal, the variable diffractive element becomes a convex lens or a concave lens due to a volume change of the liquid crystal having a large expansion coefficient compared to a solid. It can be suppressed and within the practical range.

  The electrical signal switching means switches the electrical signal applied to the variable diffractive element so that the light beam incident on the variable diffractive element becomes a main beam and two sub beams suitable for the track pitch of the information recording surface. It is possible to appropriately record or generate information on a plurality of optical recording media.

  The optical head device according to the present invention can also be applied to uses such as an optical head device, which has an advantage of realizing a plurality of diffraction gratings that can alleviate the influence of environmental temperature fluctuations with a single optical element.

1 is a diagram showing a conceptual configuration of an optical head device according to an embodiment of the present invention. Sectional drawing which shows typically an example of the structure of the variable diffraction element which comprises the optical head apparatus which concerns on embodiment of this invention. Explanatory drawing for demonstrating the electrode pattern of the transparent electrodes 23 and 24 formed in the transparent substrates 21 and 22. FIG. FIG. 4 is a diagram illustrating an example of a relationship between a voltage applied to transparent electrodes 23 and 24 constituting the variable diffraction element 2 and a change in optical path length of light transmitted through a liquid crystal 25. The figure which shows an example of the phase modulation amplitude characteristic of the transmittance | permeability and diffraction efficiency which are obtained in the variable diffraction element 2. FIG. Sectional drawing which shows typically an example of the structure of the variable diffraction element which comprises the conventional optical head apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Variable diffraction element 3 Beam splitter 4 Collimator lens 5 Aperture 6 Objective lens 7 Optical disk 7a Information recording surface 8 Photo detector 21, 22, 61, 62 Transparent substrate 23, 24, 63a, 63b, 64 Transparent electrode 25, 65 Liquid crystal 26 Sealing material 27 Flexible circuit board 60 Liquid crystal diffraction element 66 Applied voltage switching means 100 Optical head device

Claims (7)

A light source, a variable diffractive element capable of switching a diffraction pattern for diffracting a passing light beam, an objective lens for condensing light emitted from the variable diffractive element on an optical recording medium, and condensing by the objective lens And an optical head device that detects or reflects light reflected by the optical recording medium, and records or reproduces information on the optical recording medium.
The variable diffraction element has a plurality of transparent electrodes for applying an electric signal, and switches the diffraction pattern by switching the transparent electrode and applying the electric signal,
Each of the transparent electrodes is configured by alternately combining a plurality of striped electrodes on the same surface, and each set of striped electrodes can be set to a potential different from that of the other set of striped electrodes. An optical head device. A light source, an objective lens for condensing the light beam emitted from the light source on the optical recording medium, a photodetector for detecting the light beam collected by the objective lens and reflected by the optical recording medium, and from the light source to the objective lens It comprises a beam splitter that multiplexes the propagating beam and demultiplexes the beam propagating from the objective lens to the photodetector, and a variable diffractive element that can switch the diffraction pattern that diffracts the passing beam. In an optical head device for recording or reproducing information on a medium,
The variable diffractive element is disposed in at least one of the optical path between the light source and the optical recording medium and in the optical path between the optical recording medium and the optical detector, and applies a plurality of transparent signals for applying an electric signal. And having at least one of the diffraction pattern and the diffraction efficiency by switching the transparent electrode and applying the electrical signal, and each transparent electrode has a plurality of striped electrodes. An optical head device characterized in that each pair of stripe-shaped electrodes can be set to a different electric potential from that of another set of stripe-shaped electrodes.   The diffraction efficiency varies according to the diffraction pattern for switching at least one of the pitch of the diffraction grating and the direction of the stripe of the diffraction grating by switching an electric signal applied to the variable diffraction element. Optical head device.   A diffraction pattern for switching at least one of a pitch of a diffraction grating and a direction of a stripe of the diffraction grating by switching an electric signal applied to the variable diffraction element, wherein one diffraction grating of the diffraction patterns 4. The optical head device according to claim 3, wherein the pitch is infinite. The variable diffraction element is formed on at least two opposing transparent substrates, liquid crystal sandwiched between the transparent substrates, and surfaces facing the liquid crystal side of the transparent substrates, and ribbon-like electrodes are periodically A transparent electrode having a striped electrode pattern arranged in a row,
Each of the transparent electrodes is divided into two sets of striped electrodes that can be set to different potentials by electrically connecting every other ribbon-shaped electrode constituting each of the transparent electrodes. 5. The optical head device according to claim 1, wherein at least one of a pitch and a direction of the stripe-shaped electrode of the transparent substrate is different from at least one of the pitch and the direction of the stripe-shaped electrode of the other transparent substrate.   The optical head device according to claim 5, wherein an average thickness of each of the transparent substrates is 100 times or more a thickness of the liquid crystal sandwiched between the transparent substrates.   When recording or reproducing information on an optical recording medium having different track pitch standards on the information recording surface, the information recording is performed by diffracting the light beam emitted from the light source by switching the electric signal applied to the variable diffraction element. 7. The optical head device according to claim 1, further comprising an electric signal switching means for making a main beam and two sub beams suitable for a surface track pitch.

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